Portable communication devices, such as cellular telephones, personal digital assistants (PDAs), WIFI transceivers, and other communication devices transmit and receive communication signal at various frequencies. For efficient communication, the frequency of the transmit and receive signals is many times higher than the baseband information signal that carries the information to be communicated. Therefore, a transceiver must upconvert the transmit signal and downconvert the receive signal.
Usually, one or more mixers are used to upconvert the transmit signal and downconvert the receive signal. In many radio frequency (RF) communication methodologies, and in a quadrature modulation methodology in particular, a mixer can be implemented using a series of switches that switch differential components of a quadrature signal according to a local oscillator (LO) signal. The frequency of the LO signal is chosen so that a radio frequency signal mixed with the LO signal is converted to a desired frequency.
Signal upconversion and signal downconversion is performed by using mixers, which are typically implemented using semiconductor switches. In deep sub-micron technology the availability of passive switches providing low noise operation and highly efficient operating characteristics enables the use of passive mixers where low current consumption and high performance is desired. Rail to rail voltages used in the switch clock path and issues due to poor isolation between the in-phase (I) and quadrature-phase (Q) paths in the mixer impose limitations on the use of a passive mixer.